Scientists have catalogued more than one-and-a-half-million species of living organism, and they suggest there are millions more that have not yet been identified. This week's Big Question: Should we worry about extinction?

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This week's Big Question is presented by Euan McIlwraith.

What do we mean by extinction? “Most people think of extinction in terms of species - all members of a group that might get together to breed," says Dr Sue Rigby from Edinburgh University. “So extinction happens when they are all dead or functionally there are so few of them left they are incapable of generating another generation.”

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There are different kinds of extinction, she says. “You’ve got a normal extinction, because species evolve - in the way Darwin suggested - by changing and becoming better able to survive in the environment. Other species that are less well adapted become extinct. But, at the same time you have these blips where not just single species but entire systems fail. And those are the mass extinctions we see in the past and that’s what an awful lot of scientists fear is happening in the modern day.”

We should worry about the effect these extinctions might have on our planet, says Dr Bhaskar Sinha from the Ashoka Trust for Research in Ecology and the Environment in New Delhi, India.

“The first priority should be to conserve species in situ” where there is a complex interrelationship between species – microbes, bacteria, plant and animals. “It is the inter-linkages, the food chain which works together for the survival of life on the earth.”

For example, the Indian tiger is threatened with extinction. Would it matter to the local ecosystem if it died out? Bhaskar thinks it would. “The tiger is at the top of the food chain. To protect the tiger, we have to ensure that the other species on which the tiger preys upon are preserved. So in order to protect the tiger, we have to protect the entire food chain, the entire habitat.”

And Professor Phil Rainbow from the Natural History Museum in London, is worried that valuable information could be lost with the extinction of a species.

“The information we can gain about that organism, about its way of life, its metabolism, its biochemistry, all that information is in the dna (the chemical building blocks which every living creature consists of) and who knows how we might be able extract that in 50 or 100 years time? We think it would be absolutely tragic if a scientist were to turn round in 50 years time and say ‘why didn’t someone put it into a freezer?’”

So, in a project called the Frozen Ark, he preserves that dna in tissue and blood samples, and even whole organisms like snails, at -80 degrees.

Millions of life forms have existed on Earth in the 3 billion years since life began. And it’s estimated that, of them, more than 99% of species have become extinct - including the dinosaurs that lived between 230 and 65 million years ago, and the weird and exotic plants they lived among. Millions of years on and all these plants have become extinct... Or have they?

Having made their way down to the bottom of a narrow canyon some fifty metres deep, David and his friends sat down to lunch. “And that’s when I saw the Wollemi Pine. The leaves were the most striking feature. Unlike the eucalyptus or a gum tree, they were like the frond of a fern. I just pulled a small leaf off and put it in my backpack.”

A geologist recognized it from a prehistoric fossil 65 million years old. Here was a species of tree long considered extinct, which was living when the dinosaurs roamed the Earth!

If extinction is nothing new, what role is mankind playing?

Most of the extinctions through history can be put down to natural causes – like changes in the climate. But in recent centuries, mankind has caused the disappearance of a growing number of species, says Sue Rigby. “You would have to begin with over-exploitation. Polluting the environment, altering habitats so we can live there but other organisms can’t, introducing alien species that wipe out local populations, and climate change which is pushing species out of their comfortable diversity environment.”

Forty years ago, the World Conservation Union began publishing the Red Lists, surveys of the planet’s animals and plants – cataloguing how close they are to extinction. When we read that there are fewer than 6,000 Sumatran Orangutans left alive or that the Black Rhino is “Critically Endangered” that data comes from the Red Lists.

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But extinction need not be inevitable, says Erastus Lufungulo, Chief Park Warden at Arusha National Park, part of Tanzania's National Parks system. By the 1980s, extinction saw the future of the Black Rhino threatened. “This is due to the demand for rhino horn in Asia. In 1990, Tanzania launched a big anti-poaching drive and from that time, the rhino population started to increase.”

For Erastus, it is a matter of preserving resources left by previous generations and leaving them to future generations. “The second reason is economic, for we earn a lot of foreign currency from tourism. The third reason is for students and researchers.”

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Today the Black Rhino in Tanzania lives in small herds protected 24 hours a day by armed guards.

So, should we worry about extinction?

“In the long term there is probably no reason to worry about extinction. If you’re happy to play the 3-5 million year card, then I think the chances are there will be higher diversity ultimately than there is at the moment, as a consequence of wiping out a lot of species now,” says Dr Sue Rigby.

But, she says, we do have a special responsibility. “We’re aware of making moral decisions about the rights of other species to exist. So because we can define ethical systems, we have to then live within them and be concerned if we are causing the extinction of other organisms that share the earth with us.”

This edition of The Big Question was first broadcast on 12th March 2005

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